/*
 * @(#)DateAttribute.java
 *
 * Copyright 2003-2004 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   1. Redistribution of source code must retain the above copyright notice,
 *      this list of conditions and the following disclaimer.
 * 
 *   2. Redistribution in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * Neither the name of Sun Microsystems, Inc. or the names of contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MICROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
 * AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
 * DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST
 * REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL,
 * INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY
 * OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE,
 * EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 *
 * You acknowledge that this software is not designed or intended for use in
 * the design, construction, operation or maintenance of any nuclear facility.
 */

package org.wso2.balana.attr;

import java.net.URI;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.ParsePosition;
import java.text.SimpleDateFormat;

import java.util.Calendar;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;

import org.w3c.dom.Node;

/**
 * Representation of an xs:date value. This class supports parsing xs:date
 * values. All objects of this class are immutable and thread-safe. The
 * <code>Date</code> objects returned are not, but these objects are cloned
 * before being returned.
 * 
 * @since 1.0
 * @author Marco Barreno
 * @author Seth Proctor
 * @author Steve Hanna
 */
public class DateAttribute extends AttributeValue {
	/**
	 * Official name of this type
	 */
	public static final String identifier = "http://www.w3.org/2001/XMLSchema#date";

	/**
	 * URI version of name for this type
	 * <p>
	 * This field is initialized by a static initializer so that we can catch
	 * any exceptions thrown by URI(String) and transform them into a
	 * RuntimeException, since this should never happen but should be reported
	 * properly if it ever does.
	 * <p>
	 * This object is used for synchronization whenever we need protection
	 * across this whole class.
	 */
	private static URI identifierURI;

	/**
	 * RuntimeException that wraps an Exception thrown during the creation of
	 * identifierURI, null if none.
	 */
	private static RuntimeException earlyException;

	/**
	 * Static initializer that initializes the identifierURI class field so that
	 * we can catch any exceptions thrown by URI(String) and transform them into
	 * a RuntimeException. Such exceptions should never happen but should be
	 * reported properly if they ever do.
	 */
	static {
		try {
			identifierURI = new URI(identifier);
		} catch (Exception e) {
			earlyException = new IllegalArgumentException();
			earlyException.initCause(e);
		}
	};

	/**
	 * Parser for dates with no time zones
	 * <p>
	 * This field is only initialized if needed (by initParsers()).
	 * <p>
	 * NOTE: This object should only be accessed from code that has synchronized
	 * on it, since SimpleDateFormat objects are not thread-safe. If this is
	 * causing performance problems, we could easily make this a method variable
	 * in methods that use it instead of a class field. But that would mean we'd
	 * need to spend a lot more time creating these objects.
	 */
	private static volatile DateFormat simpleParser;

	/**
	 * Parser for dates with RFC 822 time zones (like +0300)
	 * <p>
	 * This field is only initialized if needed (by initParsers()).
	 * <p>
	 * NOTE: This object should only be accessed from code that has a lock on
	 * it, since SimpleDateFormat objects are not thread-safe.
	 */
	private static DateFormat zoneParser;

	/**
	 * Calendar for GMT
	 * <p>
	 * NOTE: This object should only be accessed from code that has a lock on
	 * it, since Calendar objects are not generally thread-safe.
	 */
	private static volatile Calendar gmtCalendar;

	/**
	 * Number of nanoseconds per millisecond (shared by other classes in this
	 * package)
	 */
	static final int NANOS_PER_MILLI = 1000000;

	/**
	 * Number of milliseconds per second (shared by other classes in this
	 * package)
	 */
	static final int MILLIS_PER_SECOND = 1000;

	/**
	 * Number of seconds in a minute (shared by other classes in this package)
	 */
	static final int SECONDS_PER_MINUTE = 60;

	/**
	 * Number of minutes in an hour (shared by other classes in this package)
	 */
	static final int MINUTES_PER_HOUR = 60;

	/**
	 * Number of hours in a day (shared by other classes in this package)
	 */
	static final int HOURS_PER_DAY = 24;

	/**
	 * Number of nanoseconds per second (shared by other classes in this
	 * package)
	 */
	static final int NANOS_PER_SECOND = NANOS_PER_MILLI * MILLIS_PER_SECOND;

	/**
	 * Number of milliseconds in a minute (shared by other classes in this
	 * package)
	 */
	static final int MILLIS_PER_MINUTE = MILLIS_PER_SECOND * SECONDS_PER_MINUTE;

	/**
	 * Number of milliseconds in an hour (shared by other classes in this
	 * package)
	 */
	static final int MILLIS_PER_HOUR = MILLIS_PER_MINUTE * MINUTES_PER_HOUR;

	/**
	 * Number of milliseconds in a day (shared by other classes in this package)
	 */
	static final long MILLIS_PER_DAY = MILLIS_PER_HOUR * HOURS_PER_DAY;

	/**
	 * Time zone value that indicates that the time zone was not specified.
	 */
	public static final int TZ_UNSPECIFIED = -1000000;

	/**
	 * The instant (in GMT) at which the specified date began (midnight) in the
	 * specified time zone. If no time zone was specified, the local time zone
	 * is used.
	 */
	private Date value;

	/**
	 * The time zone specified for this object (or TZ_UNSPECIFIED if
	 * unspecified). The offset to GMT, in minutes.
	 */
	private int timeZone;

	/**
	 * The time zone actually used for this object (if it was originally
	 * unspecified, the default time zone used). The offset to GMT, in minutes.
	 */
	private int defaultedTimeZone;

	/**
	 * Cached encoded value (null if not cached yet).
	 */
	private String encodedValue = null;

	/**
	 * Creates a new <code>TimeAttribute</code> that represents the current date
	 * in the default time zone.
	 */
	public DateAttribute() {
		this(new Date());
	}

	/**
	 * Creates a new <code>TimeAttribute</code> that represents the given date
	 * with default timezone values.
	 * 
	 * @param date
	 *            a <code>Date</code> object representing the instant at which
	 *            the specified date began (midnight) in the specified time zone
	 *            (the actual time value will be forced to midnight)
	 */
	public DateAttribute(Date date) {
		super(identifierURI);

		// Get the current time and GMT offset
		int currOffset = DateTimeAttribute.getDefaultTZOffset(date);
		long millis = date.getTime();

		// Now find out the last time it was midnight local time
		// (actually the last time it was midnight with the current
		// GMT offset, but that's good enough).

		// Skip back by time zone offset.
		millis += currOffset * MILLIS_PER_MINUTE;
		// Reset to last GMT midnight
		millis -= millis % MILLIS_PER_DAY;
		// Skip forward by time zone offset.
		millis -= currOffset * MILLIS_PER_MINUTE;
		date.setTime(millis);
		init(date, currOffset, currOffset);
	}

	/**
	 * Creates a new <code>DateAttribute</code> that represents the date
	 * supplied.
	 * 
	 * @param date
	 *            a <code>Date</code> object representing the instant at which
	 *            the specified date began (midnight) in the specified time zone
	 * @param timeZone
	 *            the time zone specified for this object (or TZ_UNSPECIFIED if
	 *            unspecified). The offset to GMT, in minutes.
	 * @param defaultedTimeZone
	 *            the time zone actually used for this object (if it was
	 *            originally unspecified, the default time zone used). The
	 *            offset to GMT, in minutes.
	 */
	public DateAttribute(Date date, int timeZone, int defaultedTimeZone) {
		super(identifierURI);

		init(date, timeZone, defaultedTimeZone);
	}

	/**
	 * Initialization code shared by constructors.
	 * 
	 * @param date
	 *            a <code>Date</code> object representing the instant at which
	 *            the specified date began (midnight) in the specified time
	 *            zone.
	 * @param timeZone
	 *            the time zone specified for this object (or TZ_UNSPECIFIED if
	 *            unspecified). The offset to GMT, in minutes.
	 * @param defaultedTimeZone
	 *            the time zone actually used for this object (if it was
	 *            originally unspecified, the default time zone used). The
	 *            offset to GMT, in minutes.
	 */
	private void init(Date date, int timeZone, int defaultedTimeZone) {

		// Shouldn't happen, but just in case...
		if (earlyException != null)
			throw earlyException;

		this.value = (Date) date.clone();
		this.timeZone = timeZone;
		this.defaultedTimeZone = defaultedTimeZone;
	}

	/**
	 * Returns a new <code>DateAttribute</code> that represents the xs:date at a
	 * particular DOM node.
	 * 
	 * @param root
	 *            the <code>Node</code> that contains the desired value
	 * @return a new <code>DateAttribute</code> representing the appropriate
	 *         value (null if there is a parsing error)
	 */
	public static DateAttribute getInstance(Node root) throws ParseException {
		return getInstance(root.getFirstChild().getNodeValue());
	}

	/**
	 * Returns a new <code>DateAttribute</code> that represents the xs:date
	 * value indicated by the string provided.
	 * 
	 * @param value
	 *            a string representing the desired value
	 * @return a new <code>DateAttribute</code> representing the desired value
	 *         (null if there is a parsing error)
	 */
	public static DateAttribute getInstance(String value) throws ParseException {
		Date dateValue = null;
		int timeZone;
		int defaultedTimeZone;

		if (simpleParser == null)
			initParsers();

		// If string ends with Z, it's in GMT. Chop off the Z and
		// add +0000 to make the time zone explicit, then parse it
		// with the timezone parser.
		if (value.endsWith("Z")) {
			value = value.substring(0, value.length() - 1) + "+0000";
			dateValue = strictParse(zoneParser, value);
			timeZone = 0;
			defaultedTimeZone = 0;
		} else {
			// If string ends with :XX, it must have a time zone
			// or be invalid. Strip off the possible time zone and
			// make sure what's left is a valid simple date. If so,
			// reformat the time zone by stripping out the colon
			// and parse the whole thing with the timezone parser.
			int len = value.length();

			if ((len > 6) && (value.charAt(len - 3) == ':')) {
				Date gmtValue = strictParse(zoneParser,
						value.substring(0, len - 6) + "+0000");
				value = value.substring(0, len - 3)
						+ value.substring(len - 2, len);
				dateValue = strictParse(zoneParser, value);
				timeZone = (int) (gmtValue.getTime() - dateValue.getTime());
				timeZone = timeZone / 60000;
				defaultedTimeZone = timeZone;
			} else {
				// No funny business. This must be a simple date.
				dateValue = strictParse(simpleParser, value);
				timeZone = TZ_UNSPECIFIED;
				Date gmtValue = strictParse(zoneParser, value + "+0000");
				defaultedTimeZone = (int) (gmtValue.getTime() - dateValue
						.getTime());
				defaultedTimeZone = defaultedTimeZone / 60000;
			}
		}

		// If parsing went OK, create a new DateAttribute object and
		// return it.
		DateAttribute attr = new DateAttribute(dateValue, timeZone,
				defaultedTimeZone);
		return attr;
	}

	/**
	 * Parse a String using a DateFormat parser, requiring that the entire
	 * String be consumed by the parser. On success, return a Date. On failure,
	 * throw a ParseException.
	 * <p>
	 * Synchronize on the parser object when using it, since we assume they're
	 * the shared static objects in this class.
	 */
	private static Date strictParse(DateFormat parser, String str)
			throws ParseException {
		ParsePosition pos = new ParsePosition(0);
		Date ret;
		synchronized (parser) {
			ret = parser.parse(str, pos);
		}
		if (pos.getIndex() != str.length())
			throw new ParseException("", 0);
		return ret;
	}

	/**
	 * Initialize the parser objects.
	 */
	private static void initParsers() {
		// If simpleParser is already set, we're done.
		if (simpleParser != null)
			return;

		// Make sure that identifierURI is not null
		if (earlyException != null)
			throw earlyException;

		// Synchronize on identifierURI while initializing parsers
		// so we don't end up using a half-way initialized parser
		synchronized (identifierURI) {
			// This simple parser has no time zone
			simpleParser = new SimpleDateFormat("yyyy-MM-dd");
			simpleParser.setLenient(false);

			// This parser has a four digit offset to GMT with sign
			zoneParser = new SimpleDateFormat("yyyy-MM-ddZ");
			zoneParser.setLenient(false);
		}
	}

	/**
	 * Gets the date represented by this object. The return value is a
	 * <code>Date</code> object representing the instant at which the specified
	 * date began (midnight) in the time zone.
	 * <p>
	 * <b>NOTE:</b> The <code>Date</code> object is cloned before it is returned
	 * to avoid unauthorized changes.
	 * 
	 * @return a <code>Date</code> object representing the instant at which the
	 *         date began
	 */
	public Date getValue() {
		return (Date) value.clone();
	}

	/**
	 * Gets the specified time zone of this object (or TZ_UNSPECIFIED if
	 * unspecified).
	 * 
	 * @return the offset to GMT in minutes (positive or negative)
	 */
	public int getTimeZone() {
		return timeZone;
	}

	/**
	 * Gets the time zone actually used for this object (if it was originally
	 * unspecified, the default time zone used).
	 * 
	 * @return the offset to GMT in minutes (positive or negative)
	 */
	public int getDefaultedTimeZone() {
		return defaultedTimeZone;
	}

	/**
	 * Returns true if the input is an instance of this class and if its value
	 * equals the value contained in this class.
	 * <p>
	 * Two <code>DateAttribute</code>s are equal if and only if the instant on
	 * which the date began is equal. This means that they must have the same
	 * time zone.
	 * 
	 * @param o
	 *            the object to compare
	 * 
	 * @return true if this object and the input represent the same value
	 */
	public boolean equals(Object o) {
		if (!(o instanceof DateAttribute))
			return false;

		DateAttribute other = (DateAttribute) o;

		return value.equals(other.value);
	}

	/**
	 * Returns the hashcode value used to index and compare this object with
	 * others of the same type.
	 * 
	 * @return the object's hashcode value
	 */
	public int hashCode() {
		// Only the value field is considered by the equals method, so only
		// that field should be considered by this method.
		return value.hashCode();
	}

	/**
	 * Converts to a String representation.
	 * 
	 * @return the String representation
	 */
	public String toString() {
		StringBuffer sb = new StringBuffer();

		sb.append("DateAttribute: [\n");
		sb.append("  Date: " + value + " local time");
		sb.append("  TimeZone: " + timeZone);
		sb.append("  Defaulted TimeZone: " + defaultedTimeZone);
		sb.append("]");

		return sb.toString();
	}

	/**
	 * Encodes the value in a form suitable for including in XML data like a
	 * request or an obligation. This must return a value that could in turn be
	 * used by the factory to create a new instance with the same value.
	 * 
	 * @return a <code>String</code> form of the value
	 */
	public String encode() {
		if (encodedValue != null)
			return encodedValue;

		if (timeZone == TZ_UNSPECIFIED) {
			// If no time zone was specified, format Date value in
			// local time with no time zone string.
			initParsers();
			synchronized (simpleParser) {
				encodedValue = simpleParser.format(value);
			}
		} else {
			// If a time zone was specified, don't use SimpleParser
			// because it can only format dates in the local (default)
			// time zone. And the offset between that time zone and the
			// time zone we need to display can vary in complicated ways.

			// Instead, do it ourselves using our formatDateWithTZ method.
			encodedValue = formatDateWithTZ();
		}
		return encodedValue;
	}

	/**
	 * Encodes the value of this object as an xsi:date. Only for use when the
	 * time zone is specified.
	 * 
	 * @return a <code>String</code> form of the value
	 */
	private String formatDateWithTZ() {
		if (gmtCalendar == null) {
			TimeZone gmtTimeZone = TimeZone.getTimeZone("GMT");

			// Locale doesn't make much difference here. We don't use
			// any of the strings in the Locale and we don't do anything
			// that depends on week count conventions. We use the US
			// locale because it's always around and it ensures that we
			// will always get a Gregorian calendar, which is necessary
			// for compliance with ISO 8501.
			gmtCalendar = Calendar.getInstance(gmtTimeZone, Locale.US);
		}

		// "YYYY-MM-DD+hh:mm".length() = 16
		// Length may be longer if years < -999 or > 9999
		StringBuffer buf = new StringBuffer(16);

		synchronized (gmtCalendar) {
			// Start with the GMT instant when the date started in the
			// specified time zone (would be 7:00 PM the preceding day
			// if the specified time zone was +0500).
			gmtCalendar.setTime(value);
			// Bump by the timeZone (so we get the right date/time that
			// that we want to format)
			gmtCalendar.add(Calendar.MINUTE, timeZone);

			// Now, assemble the string
			int year = gmtCalendar.get(Calendar.YEAR);
			buf.append(zeroPadInt(year, 4));
			buf.append('-');
			// JANUARY is 0
			int month = gmtCalendar.get(Calendar.MONTH) + 1;
			buf.append(zeroPadInt(month, 2));
			buf.append('-');
			int dom = gmtCalendar.get(Calendar.DAY_OF_MONTH);
			buf.append(zeroPadInt(dom, 2));
		}

		int tzNoSign = timeZone;
		if (timeZone < 0) {
			tzNoSign = -tzNoSign;
			buf.append('-');
		} else
			buf.append('+');
		int tzHours = tzNoSign / 60;
		buf.append(zeroPadInt(tzHours, 2));
		buf.append(':');
		int tzMinutes = tzNoSign % 60;
		buf.append(zeroPadInt(tzMinutes, 2));

		return buf.toString();
	}

	/**
	 * Takes a String representation of an integer (an optional sign followed by
	 * digits) and pads it with zeros on the left until it has at least the
	 * specified number of digits. Note that this function will work for an
	 * integer of any size: int, long, etc.
	 * 
	 * @param unpadded
	 *            the unpadded <code>String</code> (must have length of at least
	 *            one)
	 * @param minDigits
	 *            the minimum number of digits desired
	 * @return the padded <code>String</code>
	 */
	static String zeroPadIntString(String unpadded, int minDigits) {
		int len = unpadded.length();

		// Get the sign character (or 0 if none)
		char sign = unpadded.charAt(0);
		if ((sign != '-') && (sign != '+'))
			sign = 0;

		// The number of characters required is the number of digits,
		// plus one for the sign if present.
		int minChars = minDigits;
		if (sign != 0)
			minChars++;

		// If we already have that many characters, we're done.
		if (len >= minChars)
			return unpadded;

		// Otherwise, create the buffer
		StringBuffer buf = new StringBuffer();

		// Copy in the sign first, if present
		if (sign != 0) {
			buf.append(sign);
		}

		// Add the zeros
		int zerosNeeded = minChars - len;
		while (zerosNeeded-- != 0)
			buf.append('0');

		// Copy the rest of the unpadded string
		if (sign != 0) {
			// Skip sign
			buf.append(unpadded.substring(1, len));
		} else {
			buf.append(unpadded);
		}

		return buf.toString();
	}

	/**
	 * Converts an integer to a base 10 string and pads it with zeros on the
	 * left until it has at least the specified number of digits. Note that the
	 * length of the resulting string will be greater than minDigits if the
	 * number is negative since the string will start with a minus sign.
	 * 
	 * @param intValue
	 *            the integer to convert
	 * @param minDigits
	 *            the minimum number of digits desired
	 * @return the padded <code>String</code>
	 */
	static String zeroPadInt(int intValue, int minDigits) {
		return zeroPadIntString(Integer.toString(intValue), minDigits);
	}
}
